The Becquerel (Bq) is an SI unit of radioactivity: one becquerel is equivalent to one radioactive decay per second. That absolutely does not make it equivalent to one hertz — the random nature of radioactive decay means you’ll never get one pulse every second — but it does make it interesting. [mihai.cuciuc] certainly thought so, when he endeavored to create a clock that would tick at one becquerel.
The result is an interesting version of a Vetinari Clock, first conceived of by [Terry Pratchett] in his Discworld books. In the books, the irregular tick of the clock is used by Lord Vetinari as a form of psychological torture. For some reason, imposing this torture on ourselves has long been popular amongst hackers.
Without an impractical amount of shielding, any one-becquerel source would be swamped by background radiation, so [mihai] had to get creative. Luckily, he is the creator of the Pomelo gamma-ray spectroscope, which allowed him to be discriminating. He’s using an Am-241 source, but just looking for the characteristic 59.5 KeV gamma rays was not going to cut it at such a low count rate. Instead he’s using two of the Pomelo solid-state scintillation as a coincidence detector, with one tuned for the Am-241’s alpha emissions. When both detectors go off simultaneously, that counts as an event and triggers the clock to tick.
How he got exactly one becquerel of activity is a clever hack, too. The Am-241 source he has is far more active than one decay per second, but by varying the distance from the gamma detector he was able to cut down to one detection per second using the inverse square law and the shielding provided by Earth’s atmosphere. The result is a time signal that is a stable one hertz… if averaged over a long enough period. For now, anyway. As the Am-241 decays away, its activity decreases, and [mihai] admits the clock loses about 0.4 seconds per day.
While we won’t be giving the prize for accuracy in this contest, we are sure Lord Vetinari would be proud. The Geiger-counter sound effect you can hear in the demo video embedded below is great touch. It absolutely increases the psychic damage this cursed object inflicts.
Any cheap chinese dupes in chat?
Bravo! [hand clap]
This is illegal in most of civilized world where radioactive materials are banned. (Wink wink ruzzians with their polonium-210 tea.)
am-241 is the stuff in smoke detectors btw
Not a problem in the united states, where you can own multiple pounds (not kilograms) or something of uranium ore.
Are granite countertops illegal in your country?
Nothing about this project is illegal in the US.
I don’t know where the civilized world ends, but I strongly suspect that taking a (one, as in a single) smoke detector apart is not illegal either. Even if it is, I don’t think anyone is ever going to bother with this.
Yeah, you can probably cite some obscure regulation in an authoritarian country like the UK, but find me an actual court case based on one smoke detector.
Radioactive ore samples are available in many places in the US, such as United Nuclear and eBay.
You can purchase a card full of radioactive glow-in-the-dark watch hands on eBay. Mine came with burn marks from all the radiation.
Worth noting that the claimed 0.4s/day loss is the natural decay rate of the sample, not the actual accuracy of the clock. I really hope [mihai] keeps this running for a while so we can see how well the clock part works. I’ve been running a similar project for more than a year, and I’ve found it pretty difficult to get better than a couple hundred PPM, although I’m using a regular geiger tube.
https://hackaday.io/project/203616-atomic-clock
nice idea